Daily Archives: June 22, 2017

Viewpoint: A Roadmap for a Scalable Topological Quantum Computer – Physics

Posted: June 22, 2017 at 5:44 am

June 21, 2017• Physics 10, 68

A team of experimentalists and theorists proposes a scalable protocol for quantum computation based on topological superconductors.

Adapted from T. Karzig et al., Phys. Rev. B (2017)

The Herculean thrust to realize a quantum computer by many research groups around the world is, in my opinion, one of the most exciting endeavors in physics in quite some time. Notwithstanding the potential applications that have motivated many companies in this endeavor, a quantum computer represents the most promising avenue to peer into quantum phenomena on a macroscopic scale. As with any such great effort, the race to build a quantum computer has many competitors pursuing a variety of approaches, some of which appear to be on the verge of creating a small machine [1]. However, such small machines are unlikely to uncover truly macroscopic quantum phenomena, which have no classical analogs. This will likely require a scalable approach to quantum computation. A new study by Torsten Karzig from Microsoft Station Q, California, and colleagues [2] brings together the expertise of a large and diverse group of physicists, ranging from experimentalists to topologists, to lay out a roadmap for a scalable architecture based on one of the most popular approaches.

Karzig and colleagues paper represents a vision for the future of a sequence of developments that started with the seminal ideas of topological quantum computation (TQC) as envisioned by Alexei Kitaev [3] and Michael Freedman [4] in the early 2000s. The central idea of TQC is to encode qubits into states of topological phases of matter (see Collection on Topological Phases). Qubits encoded in such states are expected to be topologically protected, or robust, against the prying eyes of the environment, which are believed to be the bane of conventional quantum computation. This is because states of topological phases are locally indistinguishable from each other, so that qubits encoded in such states can evade the destructive coupling to the environment. But experimentally accessible topological phases of matter with the requisite properties for TQC, such as the ability to host quasiparticles known as Majorana zero modes, have been elusive. A milestone in this direction was reached in 2010, when researchers realized [57] that the combination of rather conventional ingredients, such as special semiconductors, superconductors, and magnetic fields, could result in one such phasea topological superconductor. This realization motivated experimentalists to discover signatures of this topological phase just a few years after its prediction [8]. However, the topological superconductors, or Majorana nanowires as they are often called, made in these first experiments were plagued by device imperfections such as impurities [8]. While topological robustness is supposed to protect devices from small imperfections, it is sometimes overlooked that the strength of such imperfections must be below a pretty low threshold for topological robustness to be operative.

A new wave of optimism swept the search for TQC-ready topological superconductors in 2016. Thats when experimental groups from the University of Copenhagen and from the Delft University of Technology, led by Charlie Marcus and Leo Kouwenhoven, respectively, demonstrated high-quality Majorana nanowires that were likely to be in the topological regime [9, 10]. These devices, fabricated through epitaxial growth of superconducting aluminum on indium antimonide semiconductors, showed evidence of a high-quality superconducting gap [10] and also of near energy degeneracy between the topological qubit states [9]; a large energy difference between qubit states is often related to the detrimental decoherence rate of a qubit. However, the rules of the game of designing and fabricating Majorana nanowire devices have proven to be rather different from what had been anticipated. For example, it turns out that it is quite straightforward to drive the newly fabricated devices [9] into the desirable Coulomb blockade regime (where the quantization of electronic charge dominates charge transport) but difficult to fabricate controllable contacts to connect the devices to superconducting circuitry. Interestingly, concurrent theoretical work has clarified that the topological qubit state of a Majorana nanowire can be measured via the phase shift of electron transport through the device when the transport is in the Coulomb blockade regime. This work led to suggestions that the basic operations for TQC could be performed using a procedure that relied on measurements of topological qubits.

Karzig and colleagues study comes at a point in time where there is optimism for the realization of TQC using Majorana nanowires but possibly along a path with several constraints. For example, branched structures of a nanowire could be used to generate a network of wires for TQC, but superconducting contacts are only easy to make at the ends of the wire. This would mean that superconducting contacts must be avoided in making a large network of wires. Also, the qubit lifetime will ultimately likely be limited by quasiparticle poisoning, a phenomenon in which an anomalously large number of unwanted quasiparticles, arising from Cooper electron pairs broken by stray microwaves, exists in the devices. The Karzig study brings together a large number of authors with expertise in device fabrication, in strategies for TQC, and in the solid-state-physics issues involving Majorana nanowires. The researchers propose a protocol for scalable TQC based on the existing Majorana nanowires, assuming that they can be brought into the topological phase.

The protocol involves designing a network from small sets of Majorana wires and performing a sequence of measurements on the sets (Fig. 1). The central idea is to use physical constraints on the network, such as aligning all wires with a global magnetic field, to predict which sets may be measured easily to perform TQC. For example, the researchers considered networks made from sets of four and six wires (tetron and hexon designs) together with the rule that only nearby Majorana zero modes could be measured in each configuration. They then devised a strategy for TQC that optimizes robustness to quantities such as environmental temperature and noise as well the size of the network. The result of the analysis is a few scalable architectures that future experimental groups could pick between, depending on their device-construction capabilities and computational goals. The hexon architectures are likely to be computationally more efficient than the tetron architectures but will probably be more difficult to construct.

While the scope of this work might be limited to these specific devices, detailed analysis of this kind is absolutely key to motivating both experimentalists and theorists to make progress towards a realistic platform for TQC that actually works in practice. The Karzig study likely lays the foundation for analogous work with other topological platforms as they become experimentally viable candidates for TQC. I must also clarify that the significance of this work does depend on whether future experiments meet the outstanding experimental challenges, foremost among which is the reliable generation of Majorana nanowires in a topological phase. That being said, I think Karzig and co-workers paper will serve as a case study to follow, even if the properties of topological superconducting systems turn out to be somewhat different from the ones assumed.

This research is published in Physical Review B.

Jay Sau is an Assistant Professor of Physics at the University of Maryland (UMD), College Park. He holds a B.Tech. in electrical engineering from the Indian Institute of Technology (IIT) in Kanpur, India, and a Ph.D. in physics from the University of California at Berkeley. After postdoctoral positions at UMD and Harvard University, he joined the Physics Department at UMD in 2013. His research group develops theoretical tools in condensed-matter physics to predict and understand topological phases that might one day be used to perform topological quantum computation.

Torsten Karzig, Christina Knapp, Roman M. Lutchyn, Parsa Bonderson, Matthew B. Hastings, Chetan Nayak, Jason Alicea, Karsten Flensberg, Stephan Plugge, Yuval Oreg, Charles M. Marcus, and Michael H. Freedman

Phys. Rev. B 95, 235305 (2017)

Published June 21, 2017

Torsten Karzig, Christina Knapp, Roman M. Lutchyn, Parsa Bonderson, Matthew B. Hastings, Chetan Nayak, Jason Alicea, Karsten Flensberg, Stephan Plugge, Yuval Oreg, Charles M. Marcus, and Michael H. Freedman

Phys. Rev. B 95, 235305 (2017)

Published June 21, 2017

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Viewpoint: A Roadmap for a Scalable Topological Quantum Computer - Physics

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Donald Trump Is a Crook – New York Magazine

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Donald Trump. Photo: Jim Watson/AFP/Getty Images

On November 17, 1973, President Richard Nixon delivered a speech that became famous for his self-defeating boast, I am not a crook. The windup to the infamous phrase consisted of Nixon defending his aggressive, but legal, tax-avoidance strategies. I made my mistakes, but in all of my years of public life, I have never profited, never profited from public service I have earned every cent, he insisted. (This was perhaps half-true.) And in all of my years of public life, he continued, I have never obstructed justice. (This was not true the year before, Nixon had tried to get the CIA to quash the FBI investigation into Watergate.)

Like Nixon, Donald Trump denies having engaged in obstruction of justice, even though he plainly has (both by asking intelligence agencies to push back against the FBI, according to reports, and by firing the FBI director over the Russia investigation, by Trumps own admission). Unlike Nixon, Trump does not deny profiting from public service. He does it brazenly and flamboyantly.

If he were a normal president, rather than one who produced calamities at an unprecedented pace, Trumps open profiteering would receive five-alarm media coverage and threats of impeachment. The Washington Post recently reported that Trumps budget slashes funding for a wide array of low-income housing programs, the one notable exception being a program that his own firm benefits from. The story connects this shady decision to an even shadier one: Trumps appointment of Lynne Patton a wedding planner close to the Trump family who possesses zero relevant experience and who has falsified her rsum to oversee the Department of Housing and Urban Developments programs in New York City. That is, Trump is using his budget to suspiciously single out for favoritism a program from which his firm benefits, and then installing a wildly unqualified personal loyalist in a position where she could protect his funding stream. This scandal alone could shake a non-Trump presidency to its foundations.

That it has caused barely a ripple helps to explain why Trump feels emboldened to locate the first fundraiser for his reelection campaign at his hotel in Washington. Trumps Washington hotel has already raked in cash from lobbyists and government officials, foreign and domestic, seeking to curry favor with the First Family. Trump has gotten away with it because his party has evinced zero interest in restraining him. The GOP Congress has quashed investigations of his profiteering or demands that he produce his tax returns. Now the party elite will literally be suborned at an event conjoining his public duties and the fattening of his own wallet.

History has mostly forgotten what Nixon said after his famous line: I am not a crook. I have earned everything I have got. The premise of that statement was that a president who enriches himself through office is a crook. So, what does that make Donald Trump?

A Canadian man shouted Allahu akbar and stabbed a police officer in the neck.

Her website is now dominated by short, aggregated news articles penned by other people and all manner of shady clickbait.

Iraqi and coalition forces blame ISIS; ISIS blames the U.S.-led coalition.

The Democrats arent going to take back the House by winning voters who recoil at the thought of a liberal woman from San Francisco holding power.

Mitch McConnell apparently is not any nicer than Paul Ryan.

The president wont get the meeting he asked for, chairman Cedric Richmond wrote in a letter.

Holding his first fundraiser at his own hotel is a message that the president wants to flaunt his self-enrichment.

You guys care much more about that stuff than I do, he told reporters.

All three trademark requests have been granted since the election.

But officials say the evidence indicates the attack was more spontaneous than premeditated, though the investigation continues.

Some Senate Republicans are realizing that theres a tension between solving the opioid epidemic and throwing millions of people off health insurance.

Founded with an Australian billionaire and Brett Ratner, the company was also behind Wonder Woman and Suicide Squad.

Democrats again outperformed historical markers but disappointed those looking for a breakthrough. What does that mean for 2018?

King Salman has made his ambitious and hawkish 31-year-old son next in line to the Saudi throne.

The presidents budget demands draconian cuts to public housing but maintains a subsidy to landlords that nets him millions each year.

The bus smashed into a church, several other vehicles, and sent one person to the hospital.

Declining values of three NYC office buildings are responsible for the dip.

Gone is much of peoples power to sue federal officials who engage in egregious violations of constitutional rights.

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Gergen: Special election victories show Trump could beat Dems in 2020 – CNN

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Story highlights

Republican Ralph Norman defeated Archie Parnell in Tuesday's special election for South Carolina's 5th congressional district, and in Georgia, Republican Karen Handel defeated Democrat Jon Ossoff in the most expensive House race in history. Republicans have won all four of the four special elections that have been held under President Trump.

During an appearance on CNN's "Erin Burnett Outfront," David Gergen, who advised former Presidents Richard Nixon, Gerald Ford, Ronald Reagan and Bill Clinton, admitted that off-year elections like this may not be the best predictor of what could happen in the 2018 midterms. But he said it should send a strong signal to Democrats thinking about taking back the White House.

"What's really important is that Donald Trump has seized the narrative back, that he's doing better with the voters than Democrats think he is," he said. "It should be a wake-up call for Democrats. It is possible that he could actually get re-elected if Democrats aren't careful."

Gergen has criticized Trump on a variety of issues, including his withdrawal from the Paris climate agreement and his firing of James Comey as FBI director, a fact he acknowledged during his appearance. But he said there is no doubt that "this is one occasion when we ought to say he deserves to take a victory lap."

"Any President in his shoes would do exactly what he's doing, and that is impress the voters with the fact that he withstood assaults on four different states and Republicans won all four," he added. "And you can't get away from the fact that in Georgia this was seen as a test of whether the resistance by Democrats was going to overpower the Republicans or whether the Trump vote would hold. His vote held, so this is a deserved victory lap."

The comments come as the executive director of Trump's campaign confirmed to CNN that Trump will host his first re-election campaign fundraising event next Wednesday at the Trump International Hotel in Washington, DC.

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Donald Trump talks up solar panel plan for Mexico wall – BBC News

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BBC News
Donald Trump talks up solar panel plan for Mexico wall
BBC News
US President Donald Trump has told supporters that his proposed wall along the border with Mexico could have solar panels fixed to it. Addressing a rally in Iowa, he said the panels would provide cheap energy and help to pay for the controversial wall.
Donald Trump claims attaching solar panels to Mexico border wall will ensure fortification 'pays for itself'The Independent
Donald Trump will build a solar panelled wall on the border 'to save Mexico money'Express.co.uk
Donald Trump says 'beautiful' solar panels would allow Mexico border wall to 'pay for itself'ABC Online

all 30 news articles »

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President Trump Admits He’s Not Making it Easy to Get Democrats’ Support – TIME

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President Donald Trump riffed on Democrats at his campaign-style rally in Iowa on Wednesday, saying the party has been "unbelievably nasty" while at the same time admitting he hasn't made bipartisanship easy.

I am making it a little bit hard to get their support, but who cares," Trump said Wednesday.

The President said Democrats were not willing to work with Republicans on the pending health care legislation at his Wednesday night rally, saying that even if the GOP came up with the "greatest health care plan in the history of the world" they would not get a single vote from Democrats. Democrats generally oppose the Republicans' plan to repeal the Affordable Care Act, President Obama's signature legislative achievement. And in the Senate, Republicans have been working on a bill to partner the House's replacement plan largely in secretwithout input from a large swath of members of both parties.

For a little over an hour, the President worked to convince the crowd of supporters some of whom donned "Make America Great Again" hats and held signs that his administration is making "tremendous progress" back in Washington. In signature Trump fashion, he took jabs at the "fake news media" complaining that the news cameras never show the crowds at his rallies.

Trump also couldn't help but take a little victory lap, chiding Democrats over their disappointing loss in the Georgia special election on Tuesday. After that win and the win in South Carolina, Trump said his party is "5 and 0" when it comes to special elections. "The truth is, people love us," Trump said. "All we do is win, win, win."

In his effort to rouse his supporters, Trump touted his recent announcement on changes to U.S.-Cuba policy, his decision to pull out of the Paris Climate Accords, his tax and infrastructure plans, and the tough approach his administration has taken to immigration enforcement.

On Wednesday, Trump told the Iowa crowd that the southern border wall he promised to build and make Mexico pay for could feature solar panels. "Thats one of the places that solar really does work," Trump said, noting the hot climate in the southwest, where a border wall would primarily be built. "I think we could make it look beautiful, too."

Though the President poked at Democrats, he did concede that unity on Capitol Hill would be good for the country. "Just think about what a unified American nation could achieve," he said.

During the 2016 election, many independent Iowa voters came out in support of Trump and helped him win the state. The President's Wednesday night rally marked his first trip to the state since his inauguration.

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Queen’s Speech: Donald Trump’s UK state visit in fresh doubt – BBC News

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BBC News
Queen's Speech: Donald Trump's UK state visit in fresh doubt
BBC News
Donald Trump's state visit to the UK is in fresh doubt after there was no mention of it in the Queen's Speech. The US president accepted the Queen's invitation for him to travel to Britain when Prime Minister Theresa May visited Washington in January.
Queen's Speech renews doubt over Trump's state visitCNN
Queen Elizabeth snubs Donald Trump in speech to ParliamentSalon
Trump's state visit to the UK put on hold for at least 2 years following huge protestsBusiness Insider
BuzzFeed News -POLITICO.eu -Bloomberg
all 1,035 news articles »

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Donald Trump Calls For A Law We’ve Already Had For More Than 20 Years – HuffPost

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President Donald Trumpwants Congress to pass a law denying welfare benefits to immigrants for five years.

I believe the time has come for new immigration rules which say that those seeking admission into our country must be able to support themselves financially and should not use welfare for a period of at least five years, Trump said on Wednesday night at a rally in Cedar Rapids, Iowa.

The crowd cheered wildly at this latest example of Trumps tough-on-immigrants rhetoric, and the president soaked in the applause.

However, such a law already exists.

As The Hill noted, the Personal Responsibility and Work Opportunity Reconciliation Act, which was signed into law by President Bill Clinton in 1996, prohibits immigrants from receiving federal benefits.

One section of the law is even titledRestricting Welfare and Public Benefits For Aliens, and specifically sets a five-year threshold for federal means-tested public benefit.The section carves out some exceptions for refugees and those granted asylum as well as veterans and active-duty military, their spouses and dependents.

Although its not clear how Trumps proposed law would be different, he still vowed to enact his legislation very shortly.

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Edwardsville man charged with threatening to assassinate President Trump – Belleville News-Democrat

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Belleville News-Democrat
Edwardsville man charged with threatening to assassinate President Trump
Belleville News-Democrat
An Edwardsville man posted on Facebook that he wanted to assassinate President Donald Trump, and is now facing federal charges. Joseph Lynn Pickett was charged for threatening the president of the United States on June 15. U.S. Secret Service Special ...

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Donald Trump’s New York Golf Club Seeks to Avoid Tax Bogeyman – Newsweek

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President Donald Trumps Organization wants to see its tax bill for a New York golf club cut in half. The company, which is now being run byhis sons Donald and Eric, is seeking a property tax break of $250,000 for Trump National Golf Club in Westchester, New York, town officialshave said,ABC Newsreported Wednesday.

The Trump Organization has long sought lower corporate tax bills, and its latest attempthas not been received well by local residents. It is very difficult when you see someone who has all these assets at his disposal who would rather pay lawyers to avoid his civic duty of paying taxes,Gloria Fried, a Democrat who collects taxes for Briarcliff Manor, where the course is based, told the news channel.

President Donald Trump at The Trump International Golf Links Course, Aberdeen, Scotland, on July 10, 2012. Ian MacNicol/Getty

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The Trump Organization values the course, which covers 143 acres of Westchester County, at $7.5 million, according to the report, but the town saysit should be closer to $15.1 million.Trump bought the land in 2009 for $8 million and built the 18-hole golf course, along with a housing development.

The Trump Organization has regurlarly challenged property valuations in the pastto gain tax reductions. Tax assessors rated Trump National at $15 million in 2016, while Trumps lawyers claimed it was worth just $1.35 million. Neither Trumps lawyer nor his spokesperson responded to ABCs request for comment.

The president is a big golf fan and has golf courses around the world, from Los Angeles to Scotland and Dubai.He has been photographedplayingwith world No.2 Rory McIlroy.

In April, The Independent reported that Trump had played golf 16 times since becoming president, despite promising not to play much golf. Trump criticized his predecessor President Barack Obama on Twitter for how often he played the sport.

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After five long years, San Bernardino is officially out of bankruptcy. What’s next? – Los Angeles Times

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After five years that brought major changes to San Bernardino, the struggling city is officially out of bankruptcy.

The citys plan for emerging from bankruptcy which was approved earlier this year by U.S. Bankruptcy Judge Meredith Jury became effective June 15, officials said this week. The city, facing a $45-million budget shortfall, had declared bankruptcy in August 2012.

In the years-long process since, San Bernardino has seen its fire department and other services outsourced, its staff cut by hundreds and its public services neglected. Meanwhile, it has struggled to cope with increased violence that officials have attributed in part to an under-resourced police department.

Here are some things to know about the end of the bankruptcy process, what it means for the city and what might be next.

The citys plan of adjustment became effective June 15. That means the city can begin paying its creditors under the terms outlined in that plan, which was negotiated over several years.

Its details have been known for some time.

Most significantly, the plan preserves pension benefits for employees and retirees, though employees will have to contribute more to their pension plans, benefits were modified for new employees and retirees will lose some health benefits they were promised.

Some bondholders and unsecured creditors will be paid only 1% of what they were owed.

In a memorandum on the citys most recent proposed budget, City Manager Mark Scott put it this way: While the citys momentum has improved significantly, it would be overly optimistic to suggest that decades of decline can be reversed overnight.

The bankruptcy plan, Scott noted, is very realistic in showing only modest budgetary growth over a 20-year period.

The citys poverty rate is high about 33% of its residents live in poverty and its average household income is low, making it difficult for San Bernardino to generate the revenue it needs to pay for years of backlogged services.

But city officials say they are slowly making progress toward some of their goals.

The City Council is expected to approve a $160-million operating budget for the coming fiscal year at its meeting Wednesday evening, along with a $22.6-million capital improvement budget, which will help with street repairs, city park improvements and other much-needed projects.

The operating budget also allows for some additional staff in various departments.

San Bernardino has long been affected by high levels of violence, and last year it recorded its worst homicide rate in decades. So officials have focused on boosting the police department, which saw significant staffing cuts in recent years.

Under the citys proposed budget, about $76 million has been dedicated to funding the department up from about $70 million last year.

Were gearing up to have a police department thats better resourced, Scott said in an interview Wednesday.

The city is in the process of replacing about one-quarter of an aging fleet of police vehicles, Scott said. And it is hoping to fill a large number of vacant officer positions but that is no easy goal, given the time and resources it takes to recruit and train new police officers.

The departments resources have been boosted by a number of grants, including a federal grant announced late last year to offset the cost of hiring 11 officers.

The city is also in the process of implementing a new violence reduction program, and officials are in the late stages of recruiting someone to administer it, Scott said.

City officials would like people outside the city to see its potential rather than its troubles. They tout the the fact that it is home to Cal State San Bernardino and San Bernardino Valley Community College, its relatively low-cost housing and lower costs of doing business.

As the citys proposed budget this year stated:

Opportunities for first-time home buyers, entrepreneurs, investors and employers are vast; one only needs to see the potential.

But bankruptcy has cast a cloud over many of the citys aspirations. Now that its lifted, officials are hoping outsiders will take a new look at the city.

The thing Ive run into is that people have not understood how they are going to do business with a city in bankruptcy, Scott said. They ask, Will you keep your staff? Will you be able to follow through on your obligations?

Now, he said, were able to say to people, Were like any other city.

He added: Its time for us to show off that we can be a reliable place to do business. Its up to us now to perform.

paloma.esquivel@latimes.com

Twitter: @palomaesquivel

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After five long years, San Bernardino is officially out of bankruptcy. What's next? - Los Angeles Times

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